Enhanced nitrite electroreduction to ammonia via interfacial dual-site adsorption

Abstract

The nitrite (NO2−) to ammonia (NH3) electroreduction reaction (NO2−RR) would be impeded by sluggish proton-coupled electron transfer kinetics and competitive hydrogen evolution reaction (HER). A key to improving the NH3 selectivity is to facilitate adsorption and activation of NO2−, which is generally undesirable in unitary species. In this work, an efficient NO2−RR catalyst is constructed by cooperating Pd with In2O3, in which NO2− could adsorb on interfacial dual-site through “Pd–N–O–In” linkage, leading to strengthened NO2− adsorption and easier N=O bond cleavage than that on unitary Pd or In2O3. Moreover, the Pd/In2O3 composite exhibits moderate H* adsorption, which may facilitate protonation kinetics while inhibiting competitive HER. As a result, it exhibits a fairly high NH3 yield rate of 622.76 mmol h−1 g−1cat with a Faradaic efficiency (FE) of 95.72%, good selectivity of 91.96%, and cycling stability towards the NO2−RR, surpassing unitary In2O3 and Pd/C electrocatalysts. Besides, computed results indicate that NH3 production on Pd/In2O3 follows the deoxidation to hydrogenation pathway. This work highlights the significance of H* and NO2− adsorption modulation and N=O activation in NO2−RR electrochemistry by creating synergy between a mediocre catalyst with an appropriate cooperator.